1. Field of the Invention
The present invention relates to methods and apparatus for connecting tubulars. Particularly, the invention relates an apparatus for aligning and rotating tubulars for connection therewith.
2. Description of the Related Art
In well completion operations, a wellbore is formed to access hydrocarbon-bearing formations by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annular area is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. A cementing operation is then conducted in order to fill the annular area with cement. Using apparatus known in the art, the casing string is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, one conventional method to complete a well includes drilling to a first designated depth with a drill bit on a drill string. Then, the drill string is removed and a first string of casing is run into the wellbore and set in the drilled out portion of the wellbore. Cement is circulated into the annulus behind the casing string and allowed to cure. Next, the well is drilled to a second designated depth, and a second string of casing, or liner, is run into the drilled out portion of the wellbore. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second string is then fixed, or “hung” off of the existing casing by the use of slips, which utilize slip members and cones to wedgingly fix the second string of casing in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to a desired depth. Therefore, two run-ins into the wellbore are required per casing string to set the casing into the wellbore. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.
As more casing strings are set in the wellbore, the casing strings become progressively smaller in diameter in order to fit within the previous casing string. In a drilling operation, the drill bit for drilling to the next predetermined depth must thus become progressively smaller as the diameter of each casing string decreases in order to fit within the previous casing string. Therefore, multiple drill bits of different sizes are ordinarily necessary for drilling in well completion operations.
Another method of performing well completion operations involves drilling with casing, as opposed to the first method of drilling and then setting the casing. In this method, the casing string is run into the wellbore along with a drill bit for drilling the subsequent, smaller diameter hole located in the interior of the existing casing string. The drill bit is operated by rotation of the drill string from the surface of the wellbore. Once the borehole is formed, the attached casing string may be cemented in the borehole. The drill bit is either removed or destroyed by the drilling of a subsequent borehole. The subsequent borehole may be drilled by a second working string comprising a second drill bit disposed at the end of a second casing that is of sufficient size to line the wall of the borehole formed. The second drill bit should be smaller than the first drill bit so that it fits within the existing casing string. In this respect, this method requires at least one run-in into the wellbore per casing string that is set into the wellbore.
It is known in the industry to use top drive systems to rotate a drill string to form a borehole. Top drive systems are equipped with a motor to provide torque for rotating the drilling string. The quill of the top drive is typically threadedly connected to an upper end of the drill pipe in order to transmit torque to the drill pipe. Top drives may also be used in a drilling with casing operation to rotate the casing.
More recently, gripping heads adapted for use with a top drive have been developed to impart torque from the top drive to the casing. Generally, gripping heads are equipped with gripping members to grippingly engage the casing string to transmit torque applied from the top drive to the casing. Gripping heads may include an external gripping device such as a torque head or an internal gripping device such as a spear. An example of a torque head is disclosed in U.S. Pat. No. 6,311,792, issued to Scott et al., which discloses a torque head having slips for engaging an exterior of the casing.
In addition to imparting torque to the casing, the gripping head may also provide a fluid path for fluid circulation during drilling. Generally, gripping heads define a bore therethrough for fluid communication between the top drive and the casing. Additionally, gripping heads may include sealing members to prevent leakage during circulation.
It is typically necessary to raise or lower the top drive during drilling. For example, the top drive is lowered during drilling in order to urge the drill bit into the formation to extend the wellbore. As the wellbore is extended, additional casings must be added to the casing string. The top drive is released from the casing string and raised to a desired height, thereby allowing the make up of the additional casing to the casing string.
Generally, top drives are disposed on rails so that it is movable axially relative to the well center. While the gripping head may rotate relative to the top drive, it is axially fixed relative to the top drive and thus must remain within the same plane as the top drive and well center. Because movement of the torque head and top drive are restricted, a single joint elevator attached to cable bails is typically used to move additional casings from the rack to well center.
Generally, when the casing is transported from the rack to well center, a rig hand is employed to manipulate the cable bails and angle the elevator from its resting position below the gripping head to the rack. The elevator is closed around one end of the casing to retain control of the casing. The top drive is then raised to pull the elevator and the attached casing to well center.
Once the elevator lifts the casing from the rack, the casing is placed in alignment with the casing string held in the wellbore. Typically, this task is also performed by a rig hand. Because the free end of the casing is unsupported, this task generally presents a hazard to the personnel on the rig floor as they try to maneuver the casing above the wellbore.
A pipe handling arm has recently been developed to manipulate a first tubular into alignment with a second tubular, thereby eliminating the need of a rig hand to align the tubulars. The pipe handling arm is disclosed in International Application Number PCT/GB98/02582, entitled “Method and Apparatus for Aligning Tubulars” and published on Mar. 11, 1999, which application is herein incorporated by reference in its entirety. The pipe handling arm includes a positioning head mounted on a telescopic arm which can hydraulically extend, retract, and pivot to position the first tubular into alignment with the second tubular.
Once the casings are in position, the connection is usually made up by utilizing a spinner and a power tong. Generally, spinners are designed to provide low torque while rotating the casing at a high rate. On the other hand, power tongs are designed to provide high torque with a low turn rate, such as a half turn only. While the spinner provides a faster make up rate, it fails to provide enough torque to form a fluid tight connection. Whereas the power tong may provide enough torque, it fails to make up the connection in an efficient manner because the power tong must grip the casing several times to tighten the connection. Furthermore, the action of gripping and releasing the casing repeatedly may damage the casing surface. Therefore, the spinner and the power tong are typically used in combination to make up a connection.
To make up the connection, the spinner and the power tong are moved from a location on the rig floor to a position near the well center to rotate the casing into engagement with the casing string. Thereafter, the spinner is actuated to perform the initial make up of the connection. Then, the power tong is actuated to finalize the connection. Because operating time for a rig is very expensive, some as much as $500,000 per day, there is enormous pressure to reduce the time they are used in the formation of the wellbore.
There is a need, therefore, for methods and apparatus to reduce the time it takes to make up a tubular connection. There is also a need for an apparatus for aligning tubulars for connection therewith and partly make up the connection while the power tong is moved into position.